1. Field of the Invention
The present invention generally relates to a rotary compressor and, more particularly, to an improvement in the valve cover structure of a compressor having two compression mechanisms in a sealed case.
2. Description of the Related Art
As is known, various types of compressors have been used for, e.g., refrigerators, air conditioners, and the like. A so-called two-cylinder rotary compressor is known as one of these conventional compressors. In this compressor, two rotary type compression mechanisms are incorporated in a sealed case.
According to the above rotary compressor, a motor section is arranged in the upper portion of the sealed case, and a compression mechanism section (to be described later) is arranged in the lower portion.
In the compression mechanism section, a pair of compression mechanisms are constituted by a pair of cylinders each having one end face joined to a corresponding side surface of a partition plate (spacer), a pair of rotors rotatably housed in the respective cylinders and eccentrically rotated by a crankshaft, a pair of bearings joined to the other end faces of the cylinders, a pair of discharge valves respectively arranged in the bearings, and a pair of valve covers arranged to cover the discharge valves.
The crankshaft as a rotating shaft of the motor section is coupled to the rotors. Therefore, if the motor section is operated, the respective rotors are eccentrically rotated by the crankshaft. With this operation, a gaseous refrigerant is drawn into the cylinders of the compression mechanisms by suction and compressed by the rotors. The compressed gaseous refrigerant forcibly opens each discharge valve and is discharged into each valve cover.
The gaseous refrigerant discharged into one valve cover located on the motor section side flows into the sealed case through a first path formed between the valve cover and the bearing. The gaseous refrigerant discharged into the other valve cover flows into the sealed case through a second path extending between the respective bearings joined to the pair of cylinders. With this arrangement, the gaseous refrigerant flowing into the closed case from one valve cover on the motor section side flows more easily than the gaseous refrigerant flowing into the sealed case from the other valve cover on the counter-motor section side.
In such a conventional compressor, the volume of one cover located on the motor section side is set to be substantially equal to or larger than that of the other valve cover. For this reason, the pressure of a gaseous refrigerant to be discharged into the other valve cover inevitably becomes larger than that of a gaseous refrigerant to be discharged into the first valve cover. As a result, the super compression of the other compression mechanism may be increased, or the overall compression efficiency of the compressor may be decreased because of the unbalanced compression efficiency of the pair of compression mechanisms.
In addition, if the super compression of the compression mechanism on the counter-motor section side is increased, the discharge timings of the pair of compression mechanisms may be unbalanced, resulting in degradation in noise characteristics.
As described above, in the conventional two-cylinder rotary compressor, since the volume of the valve cover on the counter-motor section side, from which a gaseous refrigerant does not easily flow into the sealed case, is substantially equal to or smaller than that of the valve cover on the motor section side, the super compression of the compression mechanism on the counter-motor section side becomes larger than that of the compression mechanism on the motor section side, resulting in a decrease in compression efficiency or degradation in noise characteristics.